Cast bar draft angle

ABSTRACT

This disclosure relates to improvements in the casting groove on the periphery of an open casting wheel. The groove is formed with a draft angle in the range of 11- 1/2 * to 14- 1/2 * which results in an average increase in casting wheel life of more than 50 percent over prior art casting wheels.

United States Patent 1 91 1111 3,818,972

1451 June 25, 1974 Berry [54] CAST BAR DRAFT ANGLE FOREIGN PATENTS ORAPPLICATIONS Inventori Milton Berry, Carrollton, 1,215,853 12/1970 GreatBritain 164/283 MT [73] Assignee: Southwire Company, Carrollton,

Ga. Primary ExaminerR. Spencer Annear [22] Filed: Oct. 5, 1972 IAttorney, Agent, or F1rm-.l-lerbert M. Hanegan; Van

C. W1lks [21] Appl. No.: 295,360

v [57] ABSTRACT [2%] :JSIll. l64/;372,2ld6 11/127)?5 This disclosurerelates to improvements in the casting 'l i 283 groove on the peripheryof an open casting wheel. The l 1 o earc l groove is formed with a draftangle in the range of 56 R f d l 1- /2 to l4-/2 which results in anaverage increase in l 1 e erences casting wheel life of more than 50percent over prior UNITED STATES PATENTS an Casting whee|5 3,429,3632/1969 Hazelett et a1 164/87 4 Claims, 6 Drawing igures 3,536,12610/1970 Lenaeu et al 164/278 CAST BAR DRAFT ANGLE This invention relatesto the metal forming arts, and more particularly to the continuouscasting of molten copper and other metals by means of a casting wheelhaving a casting groove formed in the periphery thereof.

In the preparation of a metal rod or wire product by means of acontinuous casting and rolling operation, molten metal is continuouslycast into a continuous bar by a continuous casting machine and then,substantially immediately thereafter, hot-worked in a rolling mill toyield a continuous rod. The rod may then be cold drawn through a seriesof dies to form wire.

A typical continuous casting machine includes a conventional castingwheel having a casting groove in its periphery which is partially closedby an endless belt supported by the casting wheel and at least one idlerpulley. The casting wheel and the endless belt cooperate to provide amold into one end of which molten metal is poured to solidify and fromthe other end of which the cast bar is emitted in substantially thatcondition in which it solidified. Examples of such continuous castingmachines are disclosed in US. Pat. Nos. 3,279,000 and 3,336,972, issuedto D. B. Cofer et al. and assigned to the assignee of this invention.

The peripherally circumferential casting groove formed in conventionalcasting wheels has two side walls and a bottom surface or floorextending therebetween. In radial cross-section, the side walls inwardlyconverge toward the radial axis of the wheel. The

slightly obtuse angle defined between each of the side 7 walls and thebottom surface facilitates paying out of the cast bar from the groove.The amount that this angle exceeds 90, or the angle subtended by each ofthe side walls and the radial axis of the wheel, is termed the draftangle of the wheel. Heretofore, the draft angle of conventional castingwheels has been approximately 9/2.

During the normal casting operation, molten metal will tend to depositand accumulate on the interior forming walls of the casting groove.Moreover, particularly during the casting of copper in'a steel wheel,the thermal loading of the wheel resulting from the depositing of moltenmetal thereon and the simultaneous operation of cooling it into a castsolid bar causes the side walls of the casting groove to close in,thereby reducing the draft angle of the casting groove and causing thecast bar to stick in the wheel. This condition obviously hinders thenormal pay-out operation necessary to the continuous casting process, aswell as causes severe mechanical stresses on the casting groove whichresults in surface cracking that seriously shortens the useful life ofthe casting wheel. This condition may be further aggravated by thetension of the endless belt on the mold walls.

Qualitatively, the situation can be described step-bystep, as follows:

1. Molten metal is poured into a relatively cold mold. The mold deflectsdue to thermal stresses caused by the molten metal. Simultaneously, athin, weak shell is formed around the cast metal section. The moldcavity is then larger than it was prior to pourmg.

2. The shell then becomes thicker and shrinks away from the mold someamount creating a gap which decreases heat flow away from the mold andallows the mold to shrink, reversing the deflection and heat flowprocess.

3. Towards the end of the cycle, heat transfer gradually decreases withaccompanying decrease in mold temperature and mold temperaturegradients. This causes the mold to close in with dimensions smaller thanat the beginning of the cycle, with consequent contact and sometimessticking between the sides of the mold and the cast bar.

4. As the bar is then continuously extracted from the mold, the moldtemperature gradually reaches some steady value approximately equal tothe initial temperature when the pour was made.

It has been determined that with a casting wheel having a standard draftangle of 9% as used in the industry, the close in described in steps 2and 3 above will result in the draft angle being reduced toapproximately 8 /2" at that point in time, thereby seriously hinderingthe pay-out of the cast bar and setting up severe mechanical stresses inthe casting wheel.

It is, therefore, a primary object of this invention to provide acasting wheel having an increased useful life.

Another object of this invention is to provide a casting wheel whichfacilitates extraction of the cast bar therefrom.

A further object of this invention is to provide a casting wheel havinga casting groove that inhibits the tendencies of close in and surfacecracking.

More particularly, it is an object of this invention to provide acasting wheel for use in a continuous casting operation wherein theperipheral casting groove has a draft angle that will not decrease belowapproximately 9 /z throughout the entire thermal cycle in a normalcasting operation. In accordance with this invention, the foregoingobjects and others that may hereinafter become apparent are accomplishedby providing a casting wheel having a casting groove with a draft anglein the range of from approximately 1 l'/2 to approximately l4%,preferably approximately 12. It has been determined in accordance withthis invention that a casting groove having a draft angle in the rangeof l 1%" to 14% will not decrease below approximately 9% throughout anyportion of the thermal cycle in a normal casting operation.Consequently, the tendency of the cast bar to stick in the castinggroove is significantly reduced thereby facilitating easier pay-out anda corresponding increase in the life of the wheel. It has been foundthat casting wheels constructed in accordance with this invention haveexhibited an average increase in useful life of more than fifty percentover the life of prior art casting wheels having draft angles of 9V2.

While the lower limit of ll l is considered critical for the foregoingreasons, the upper limit of 14%" is also considered significant andcritical. To begin with, for structural reasons that will becomehereinafter apparent, any increase in the draft angle necessitates anincrease in the wall thickness of the mold where the outside surface ofthe mold remains perpendicular to the axis of rotation of the mold witha corresponding decrease in the heat transfer rate out of the mold andthus a decrease in the production rate. Therefore, it has been found tobe advantageous to fabricate the casting mold so that mold'side wallthickness is essentially uniform. It has been found that the decrease inthe heat transfer rate is acceptable with draft angles up to l4%.

Moreover, as the draft angle increases, the crosssectional shape of thecast bar deviates to a greater extent from a rectangular shape which isless desirable for the rolling operation. Accordingly, the 14% limit hasbeen determined to yield a bar having a cross-sectional shape that isstill acceptable for the rolling operation. The preferable draft angleof 12 has been found to be an optimum in that it facilitates extractionof the bar from the groove while not unduly increasing the heat transferrate nor yielding a shape that is undesirable for the rolling operation.

With the above and other objects in view that may hereinafter becomeapparent, the nature of the invention may be more clearly understood byreference to the several views illustrated in the accompanying drawing,the following detailed description thereof, and the appended claimedsubject matter:

IN THE DRAWINGS FIG. 1 is a highly-schematic elevation view of apparatussuitable to continuously manufacture rod, including a continuous castingmachine and a rolling mill having a plurality of roll stands; I

FIG. 2 is an enlarged radial sectional view taken along line 22 of FIG.1, and illustrates a prior art casting groove having a draft angle of 9%which has cracks, ripping and metal build-up formed on the wallsthereof;

FIG. 3 is a radial sectional view of one embodiment of a casting grooveformed in accordance with this invention, and illustrates the walls ofthe groove being broken, the lower portion having a draft angle of 9%and the upper portion having a draft angle of 14%";

FIG. 4 is a radial sectional view of the preferred embodiment of acasting groove formed in accordance with this invention, and depicts thegroove having a draft angle of 12;

v FIG. 5 illustrates the geometric relationship between a wedge and twoinclined planes wherein the friction therebetween can be compared to thefriction between a cast bar and a casting groove; and

FIG. 6 illustrates the normal forces and friction forces acting on acast bar in a casting groove mold.

Referring now to the drawings in detail, there is illustrated apparatusfor continuously manufacturing rod from molten copper and other metals.The apparatus includes a continuous casting machine generally designatedby the numeral 10, and a rolling mill generally designated by thenumeral 11.

The continuous casting machine 10 serves as a casting means forsolidifying molten metal M to provide a cast metal such as a cast bar 12that is conveyed in substantially that condition in which it solidifiedfrom the continuous casting machine 10 to the rolling mill 11 whichserves as a hot-forming means for hot-forming the cast bar 12 into rod16 or another hot-formed prod- LlCt.

The continuous casting machine 10 is of conventional casting wheel typesimilar to that shown in US. Pat. No. 3,336,972 and has a casting wheel13 with a casting groove partially closed by an endless band 14 which issupported against the casting wheel 13 by a plurality of idler wheels15. The casting wheel 13 and endless band 14 cooperate to provide a moldinto one end of which molten metal M is poured to solidify and from theother end of which the cast bar 12 passes in substantially thatcondition in which it solidified.

The rolling mill 11 is of conventional type having a plurality of rollstands 17 arranged to hot-form the cast metal by a series of successivedeformations. The continuous casting machine 10 and the rolling mill 11are positioned relative to each other so that the cast bar 12 enters therolling mill 11 substantially immediately after solidification so as tobe in substantially that condition in which it solidified and at ahot-forming temperature within the range of temperatures for hotformingthe cast bar 12. No heating of the cast bar 12 is required between thecasting machine 10 and the rolling mill ll but,in the event that it isdesired to closely control the hot'forming temperature of the cast bar12, means for adjusting the temperature of the cast bar 12 may be placedbetween the continuous casting machine 10 and the rolling mill 11without departing from the inventive concept disclosed herein.

It will be understood that with the apparatus of FIG. 1, the cast bar 12may be of any one of a plurality of lengths determined only by theamount of molten metal M solidified and may extend between thecontinuous casting machine 10 and the rolling mill 11. Thus, the stepsof solidifying molten metal to obtain cast metal and of hot-forming thecast metal are generally being performed simultaneously once theapparatus of FIG. 1 is in operation.

Referring to FIG. 2, there is illustrated in radial crosssection a priorart mold 20 heretofore formed in the periphery of conventional castingwheels. The mold 20 includes a casting groove 21 defined by side walls22, 23 and a bottom surface or floor 24 extending therebetween. Each ofthe side walls 22, 23 defines a slightly obtuse angle with the floor 24.The amount that this angle exceeds is termed the draft angle a of themold. The draft angle a can also be defined as the angle subtended byeach of the side walls 22, 23 with the radial axis of the casting wheel13. As was heretofore standard in the industry, the draft angle a of theprior art mold 20 is 9%.

As seen in FIG. 2, a build-up of metal 25 has formed on the side wall 22which will tend to make the cast bar 12 stick in the mold 20 and thushinder the normal payout or extraction process. The build-up or swellingcaused by the metal 25 will further add to the close in effect that isevident during the thermal cycle in the casting operation. Also presentin the prior art mold 20 are cracks and ripping formations 26 formed inthe floor 24 and side wall 23. The cracks and ripping formations 26represent, of course, failures in the mold 20 caused by the stresses setup therein as a result of the cast bar 12 sticking in the mold 20 andthe friction forces developed as the cast bar 12 is extracted therefrom.

The relationship between the draft angle a and the friction force fbetween a casting and the sides of a casting wheel is analogous to awedge contained between inclined planes and having friction on thecontacting surfaces as illustrated in FIG. 5. Analyzing thetrigonometric relationships wherein F normal force and p. coeffient offriction:

From statics Then, for free motion between planes and wedge Completingthe analogy with respect to a casting in a mold as seen in FIG. 6:

From statics 2F=O=2Nsina-2uNcosa Then, for free motion between thecasting and mold p, tan a a tan p.

It should be apparent, therefore, both in view of the foregoing analysisand from empirical evidence that there is a direct physical relationshipbetween the draft angle and the friction force between the cast bar andthe sides of the casting wheel. It has been determined in accordancewith the invention that increasing the draft angle a to at least 11%?will reduce the friction force sufficiently to permit extraction of thecast bar from the casting wheel throughout the entire casting operationwithout significant sticking and consequent stress and failure of thecasting wheel.

A preferred embodiment of the invention is illustrated in FIG. 4 whereinthere is depicted a mold 30 having a draft angle a of 12. Not only willthe increased draft angle a of 12 reduce friction and stress, but theclose in effect during thermal loading will not reduce the draft anglebelow 9%", thereby preventing further sticking of the'cast bar in themold.

It should be apparent, however, that while the draft angle a of the mold30 has been increased, the wall thickness of the mold 30 has beenconcomitantly increased to accommodate the increased draft angle.Consequently, the heat transfer rate out of the mold, and thus theproduction rate of the casting wheel, will be reduced. It has beendetermined that while a draft angle of 12 is an optimum, draft angles upto l4% can be tolerated without undue reduction in the heat transferrate.

Referring now to FIG. 3, there is illustrated a mold 40 which representsanother embodiment of the invention. The mold 40 includes a castinggroove 41 having a floor 42 and broken side walls having angularlydisposed sections 43, 44 and 45, 46, respectively. While the lower sidewall sections 44 and 46 define a conventional draft angle a of 9%", theupper wall sections 43 and 45 define a draft angle a, of 14%. In thismanner,

improved extraction of the cast bar is facilitated while the heattransfer rate, and thus the production rate, is not diminished. I

It should be understood that while the draft angle a of the mold 30 andthe draft angle a, of the mold 40 have been specifically describedherein as 12 and 14%", respectively, it is contemplated that the rangeof either angle may vary from about 1 l% to about l4% within the scopeof this invention. 5 It should be apparent. therefore, that there isprovided in accordance with this invention an improved casting wheel foruse in a continuous casting operation wherein provideda draft angle inthe range of l l% to 14% will facilitate extraction of the cast bar fromthe mold thereby reducing stresses and increasing the useful life of thecasting wheel.

While the invention has been specifically illustrated and describedherein with reference to preferred embodiments thereof, it iscontemplated that minor modifications could be made without departingfrom the spirit of the invention.

It is claimed:

1. In a casting wheel having an open casting groove formed in theperiphery thereof, said casting groove being defined by two side wallsand a floor extending therebetween and wherein each of said side wallssubtends a draft angle with the radial axis of said wheel; theimprovement comprising providing said draftangle in the range of fromabout ll% to about 14%.

2. A casting wheel as defined in claim I wherein said draft angle isabout 12.

3. A casting wheel as defined in claim 1 wherein each of said side wallsincludes an upper section and a lower section, and wherein each of saidsections subtends a different draft angle with the radial axis of saidwheel.

4. A casting wheel as defined in claim 3 wherein the draft anglesubtended by said upper section is greater than the draft anglesubtended by said lower section.

5. In a casting wheel having an open casting groove formed in theperiphery thereof, said casting groove being defined by two side wallsand a floor extending therebetween and wherein each of said side wallssubtends a draft angle with the radial axis of said wheel; said sidewalls including an upper section and a lower section, said lower sectionsubtending a draft angle of about 9% and said upper section subtending adraft angle of from about Il% to about 14%".

6.'A casting wheel as defined in claim 5 wherein the draft anglesubtended by said upper section is about l4%.

7. In a casting wheel for solidifying a molten metal in a peripheralgroove defined by a bottom surface and by two side walls extendingradially beyond said bottom surface, a side wall having an inner surfacewith at least a portion thereof in a first plane of reference whichforms an angle with a second plane of reference that includes saidbottom surface, said side wall being of a thickness and of a castingwheel metal that are such that said side wall is distorted in shape inresponse to the heat of a molten metal in said peripheral groove tocause said angle to decrease by an amount less than a predeterminedmaximum, and being shaped so that in the absence of said heat, saidangle is greater than a predetermined minimum by said predeterminedmaximum.

8. The casting wheel of claim 7 in which said casting wheel metal issteel, said molten metal is copper, and said predetermined minimum is99%.

9. In a casting machine for solidifying a molten metal in a castingcavity defined by a casting wheel having a bottom surface and two sidewalls extending radially beyond said bottom surface and by a band urgedagainst the outermost edges of said side walls with a predeterminedforce, a casting-wheel with a bottom surface and side wall having aninner surface with at least a portion thereof in a first plane ofreference which forms an angle with a second plane of reference thatincludes said bottom surface, said side wall being of a thickness and ofa casting wheel metal that are such that said side wall is distorted inshape by said band and by the heat of a molten metal in said peripheralgroove to cause said angle to decrease by an amount less than apredetermined maximum, and being shaped so that in the absence of saidheat and said band, said angle is greater than a predetermined minimumby said predetermined maximum.

10. The casting machine of claim 9 in which said casting wheel metal issteel, said molten metal is copper, and said predetermined minimum is 99/2.

11. In apparatus for continuously casting a bar from a molten metalcomprising a casting wheel having a peripheral groove defined by twoside walls and a bottom surface extending therebetween and constructedof a given metal, each of said side walls subtending a draft angle withthe radial axis of said wheel, said peripheral groove being constructedaccording to the formula:

a tanu where (or) represents the draft angle and t) represents thecoefficient of friction between said bar and said given metalconstituting said side walls.

12. The apparatus of claim 11 wherein said given metal from which saidperipheral groove is constructed is steel, and wherein said draft angleis in the range of from about 11% to about 14% when the molten metalintended to be cast is copper.

13. in a method of continuously casting molten copper in a casting wheelhaving a peripheral groove formed from steel and defined by two sidewalls and a bottom surface extending therebetween and wherein each ofthe side walls subtends a draft angle with the radial axis of thewheel,pouring the molten copper into the groove thereby causing thermalexpansion of the groove and an increase in the initial draft angle,cooling and solidifying the molten copper in the groove causing adecrease in the draft angle to a value less than the value of the draftangle existing prior to the pouring of the molten copper, and extractingthe solidified copper from the groove; the improvement comprising:

providing a casting wheel having a groove constructed with a draft angleexisting prior to the pouring of the molten copper which exceeds by apredetermined amount the draft angle existing after the cooling andsolidifying of the molten copper, said predetermined amount beingselected such that the draft angle existing after the cooling andsolidifying of the molten copper will not be less than a predeterminedminimum value which readily permits extraction of the solidified copperfrom the groove.

14. The method of claim 13 wherein said predetermined minimum value is9% and said predetermined amount by which the draft angle existing priorto the pouring exceeds the draft angle existing after the cooling andsolidifying is from about 2 to about 5.

1. In a casting wheel having an open casting groove formed in theperiphery thereof, said casting groove being defined by two side wallsand a floor extending therebetween and wherein each of said side wallssubtends a draft angle with the radial axis of said wheel; theimprovement comprising providing said draft angle in the range of fromabout 11 1/2 * to about 14 1/2 * .
 2. A casting wheel as defined inclaim 1 wherein said draft angle is about 12* .
 3. A casting wheel asdefined in claim 1 wherein each of said side walls includes an uppersection and a lower section, and wherein each of said sections subtendsa different draft angle with the radial axis of said wheel.
 4. A castingwheel as defined in claim 3 wherein the draft angle subtended by saidupper section is greater than the draft angle subtended by said lowersection.
 5. In a casting wheel having an open casting groove formed inthe periphery thereof, said casting groove being defined by two sidewalls and a floor extending therebetween and wherein each of said sidewalls subtends a draft angle with the radial axis of said wheel; saidside walls including an upper section and a lower section, said lowersection subtending a draft angle of about 9 1/2 * and said upper sectionsubtending a draft angle of from about 11 1/2 * to about 14 1/2 * .
 6. Acasting wheel as defined in claim 5 wherein the draft angle subtended bysaid upper section is about 14 1/2 * .
 7. In a castiNg wheel forsolidifying a molten metal in a peripheral groove defined by a bottomsurface and by two side walls extending radially beyond said bottomsurface, a side wall having an inner surface with at least a portionthereof in a first plane of reference which forms an angle with a secondplane of reference that includes said bottom surface, said side wallbeing of a thickness and of a casting wheel metal that are such thatsaid side wall is distorted in shape in response to the heat of a moltenmetal in said peripheral groove to cause said angle to decrease by anamount less than a predetermined maximum, and being shaped so that inthe absence of said heat, said angle is greater than a predeterminedminimum by said predetermined maximum.
 8. The casting wheel of claim 7in which said casting wheel metal is steel, said molten metal is copper,and said predetermined minimum is 99 1/2 * .
 9. In a casting machine forsolidifying a molten metal in a casting cavity defined by a castingwheel having a bottom surface and two side walls extending radiallybeyond said bottom surface and by a band urged against the outermostedges of said side walls with a predetermined force, a casting wheelwith a bottom surface and side wall having an inner surface with atleast a portion thereof in a first plane of reference which forms anangle with a second plane of reference that includes said bottomsurface, said side wall being of a thickness and of a casting wheelmetal that are such that said side wall is distorted in shape by saidband and by the heat of a molten metal in said peripheral groove tocause said angle to decrease by an amount less than a predeterminedmaximum, and being shaped so that in the absence of said heat and saidband, said angle is greater than a predetermined minimum by saidpredetermined maximum.
 10. The casting machine of claim 9 in which saidcasting wheel metal is steel, said molten metal is copper, and saidpredetermined minimum is 99 1/2 * .
 11. In apparatus for continuouslycasting a bar from a molten metal comprising a casting wheel having aperipheral groove defined by two side walls and a bottom surfaceextending therebetween and constructed of a given metal, each of saidside walls subtending a draft angle with the radial axis of said wheel,said peripheral groove being constructed according to the formula:Alpha > tan 1 Mu where ( Alpha ) represents the draft angle and ( Mu )represents the coefficient of friction between said bar and said givenmetal constituting said side walls.
 12. The apparatus of claim 11wherein said given metal from which said peripheral groove isconstructed is steel, and wherein said draft angle is in the range offrom about 11 1/2 * to about 14 1/2 * when the molten metal intended tobe cast is copper.
 13. In a method of continuously casting molten copperin a casting wheel having a peripheral groove formed from steel anddefined by two side walls and a bottom surface extending therebetweenand wherein each of the side walls subtends a draft angle with theradial axis of the wheel, pouring the molten copper into the groovethereby causing thermal expansion of the groove and an increase in theinitial draft angle, cooling and solidifying the molten copper in thegroove causing a decrease in the draft angle to a value less than thevalue of the draft angle existing prior to the pouring of the moltencopper, and extracting the solidified copper from the groove; theimprovement comprising: providing a casting wheel having a grooveconstructed with a draft angle existing prior to the pouring of themolten copper which exceeds by a predetermined amount the draft angleexisting after the cooling and solidifying of the molten copper, saidpredetermined amount being selected such that the draft angle existingafter the cooling and solidifying of the molten copper will not be lessthan a predetermined minimum value which readily permits extraction ofthe Solidified copper from the groove.
 14. The method of claim 13wherein said predetermined minimum value is 9 1/2 * and saidpredetermined amount by which the draft angle existing prior to thepouring exceeds the draft angle existing after the cooling andsolidifying is from about 2* to about 5* .